Inverter grid synchronisation – Six AC system frequency facts

With inverter grid synchronisation the key problem is that the grid frequency can vary. In fact the frequencies of AC systems around the world are different and they are also constantly changing. This makes it a challenge to connect renewable generation to the network.

AC System Frequency

Aircraft AC systems run at 400Hz three phase. They do this to make the motors lighter with less iron due to the volt second integral being lower.

Some railway locomotive AC systems are 16.7Hz single phase. These frequencies are chosen to minimise the current needed to charge the capacitance of the overhead line and so minimises the number of substations needed. The 16.7Hz is chosen to so as to not be a multiple of 50Hz. The was made by rotary frequency changers (this is truly what they were called as power engineers often lack imagination) but is now also made by static power electronic frequency changers. With modern static frequency changers with inverter grid synchronisation 16.7Hz is achieved.

In Switzerland the railway has their own separate distribution grid.

There have been railway frequencies as low as 8Hz and some train locomotives even operate from very low frequency AC with a frequency of zero. DC is the AC you have when you are not having AC.

Early on GE decided that 40Hz would be good for AC distribution but it did not catch on.

There are aluminium smelters in Australia where they have or had 60Hz, 50Hz, 25Hz and 16 2/3 Hz AC systems and reportedly all at the same time.